I'm thinking it can be a general ability common to cairns (i.e. the Cairn Wraith and Dodkong could have it to). Which'd go some way to explain why the Dodkong's so elusive and has survived so long: he can feel living intruders coming and avoids them.
Got a few ideas to make it a little more interesting, but don't have the time or inclination at the moment as I've spent long enough on those blinkin' Dragon Warriors for today.
Might post something in a day or three.
Let's have a stab at this, in order of increasing elaborateness:
Detect Life #1—Life Detection. The cairn knows if there is a living creature within 300 feet of it, as well as the creature's type (beast, humanoid, et cetera), and degree of sentience (mindless, animal intelligence, or fully sapient). The cairn can use an action to focus Detect Life on a creature it senses, which lets the cairn know where the creature is located. This power can penetrate most barriers, including any thickness of rock or dirt, but is blocked by 1 inch of common metal, a thin sheet of lead, or 3 feet of wood.
Detect Life #2—Sense Life. The cairn knows if there is a living creature within 300 feet of it, as well as the creature's type (beast, humanoid, et cetera), and degree of sentience (mindless, animal intelligence, or fully sapient). The cairn can use an action to focus Sense Life on a living creature it detects, which must make a DC ## Wisdom saving throw. If the target fails, the cairn knows where the creature is located. If the target succeeds, then for the next 24 hours the targeted creature gets a chilling impression they're being watched every time the cairn focuses Sense Life upon them; the target can then make a Wisdom (Insight) check or Charisma (Deception) check against a Wisdom (Perception) check by the cairn; if this check succeeds the cairn's Sense Life will not locate that creature for 1 minute, or until the cairn locates them with another sense.
This power can penetrate most barriers, including any thickness of rock or dirt, but is blocked by 1 inch of common metal, a thin sheet of lead, or 3 feet of wood.
Detect Life #3—Life Sense. The cairn can sense living organisms within 300 feet of it. If a living creature enters this range, it must succeed on a Wisdom saving throw against the cairn's passive Perception (DC ##); if the creature fails, the cairn is alerted to the creature's presence, as well as the creature's type (beast, humanoid, et cetera), and degree of sentience (mindless, animal intelligence, or fully sapient). If the creature succeeds, the cairn's Life Sense will not detect them for 1 minute (whereupon the creature repeats the saving throw), or until the cairn notices the intruder using one of its other senses (which causes Life Sense to automatically detect the creature).
The cairn can use an action to focus Life Sense on a living creature it detects, which must make a DC ## Wisdom saving throw. If the target fails, the cairn knows where the creature is located. If the target succeeds, then for the next 24 hours the targeted creature gets a chilling impression they're being watched every time the cairn focuses Life Sense at them; the target can then make a Wisdom (Insight) check or Charisma (Deception) check against a Wisdom (Perception) check by the cairn; if this check succeeds the cairn's Life Sense will not locate that creature for 1 minute, or until the cairn locates them with another sense.
This power can penetrate most barriers, including any thickness of rock or dirt, but is blocked by 1 inch of common metal, a thin sheet of lead, or 3 feet of wood.
Mixed up the names so it wasn't just
Detect Life #1,
#2 and
#3. Of the three names I like
Life Sense the best (or should that be
Lifesense?), although not necessarily the
Detect Life #3 "Life Sense" ability.
I've got an idea for an
even more complicated version, but that'll have to wait.